Don't complain as much about convincing demonstration (6,6)
I believe the answer is:
object lesson
'demonstration' is the definition.
(thesaurus)
'don't complain as much about convincing' is the wordplay.
I cannot really understand how this works, but
'complain' could be 'object' (to object to something) and 'object' is found in the answer.
'as' could be 'so' (I've seen this in other clues) and 'so' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for object lesson that I've seen before include "Example typifying a principle" , "punishment intended as a warning to others?" , "What may be striking" , "Instructive experience" , "shows what one should do" .)